Biology

Cellular Respiration and Enzymes

1,721 Questions

Explore key concepts of cellular respiration, including glycolysis, the Krebs cycle, and the electron transport chain. These questions also cover ATP production, anaerobic respiration, and essential metabolic pathways. This topic forms a core part of the biology syllabus for many competitive examinations.

Glycolysis and metabolic pathwaysKrebs cycle processesElectron transport chainATP production countAnaerobic respiration products

Cellular Respiration and Enzymes Questions

Multiple choice

Energy is stored in the cells as

  1. ATP

  2. DNA

  3. NADP

  4. None of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

ATP (Adenosine Triphosphate) is the primary energy storage molecule in cells. DNA stores genetic information, NADP is involved in photosynthesis, and ATP is the universal energy currency.

Multiple choice

Various inhibitors are used in the study of the electron transport system at various levels of electron carriers.

Which of the following substances acts as an inhibitor of the electron transport system between the flavoproteins and coenzyme Q?

  1. Atractyloside

  2. Bactoprenol

  3. Amytal

  4. Azurin

  5. Antimycin A
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Amytal (5-ethyl-5-isoamylbarbituric acid) is a barbiturate drug that inhibits the electron transport system between the flavoproteins and coenzyme Q.

Multiple choice

When one molecule of FADH2 is oxidised to FAD, the number of ATP produced is

  1. one

  2. two

  3. three

  4. four

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In the electron transport chain, each FADH2 molecule yields approximately 1.5 to 2 ATP molecules (modern estimates use 1.5, older textbooks used 2). FADH2 enters the chain at Complex II (coenzyme Q), bypassing Complex I, so it pumps fewer protons and generates less ATP than NADH, which yields 2.5 to 3 ATP.

Multiple choice

What is the energy currency of a cell?

  1. GTP

  2. ATP

  3. ADP

  4. NADP
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Energy is usually liberated from the ATP molecule to do work in the cell by a reaction that removes one of the phosphate-oxygen groups, leaving adenosine diphosphate (ADP).

Multiple choice

Consider the following statements:

  1. Beta-oxidation takes place only in glyoxysomes and not in cytosol.
  2. When fatty acids undergo beta oxidation to form Acetyl CoA, only NADH is produced and not FADH2. Which of the statements given above is/are correct?

  1. 1 only

  2. 2 only

  3. Both 1 and 2

  4. Neither 1 nor 2
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Statement 1 is incorrect because beta-oxidation occurs in mitochondria (not glyoxysomes) in animals, and in glyoxysomes in plants, not 'only' in glyoxysomes. Statement 2 is also incorrect because beta-oxidation produces BOTH NADH and FADH2, not just NADH. Each cycle produces one NADH, one FADH2, and one acetyl-CoA. Therefore BOTH statements are wrong, making option D correct.

Multiple choice

Consider the following statements :

  1. The Penthose Phosphate Pathway supplies Erythrose-4-Phosphate which is the starting material in the synthesis of lignin.
  2. The Pentose Phosphate Pathway also occurs in plastids.
  3. NADPH is generated by the Pentose Phosphate Pathway. Which of the statements given above are correct?

  1. 1 and 2 only

  2. 2 and only

  3. 1 and 3 only

  4. 1,2 and 3
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Pentose Phosphate Pathway produces erythrose-4-phosphate which is precursor for aromatic amino acids and lignin synthesis. PPP operates in plastids (including chloroplasts). NADPH is generated as oxidative phase product. All three statements are correct.

Multiple choice

Which one of the following is the correct sequence of the appearance of intermediate compounds in the pathway of photorespiration ?

  1. Glyoxylate - glycine - glycolate - serine

  2. Glyoxylate - serine - glycolate - glycine

  3. Glycolate - glyoxylate - glycine - serine

  4. Glycolate - glyoxylate - serine - glycine
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Photorespiration begins when RuBP oxygenase produces phosphoglycolate, which is converted to glycolate. Glycolate exits chloroplasts, enters peroxisomes, and is converted to glyoxylate. Glyoxylate then transaminates to glycine. Glycine enters mitochondria, where two molecules combine to form serine, releasing CO2 and NH3. Thus the sequence is: Glycolate → glyoxylate → glycine → serine.